Calcium mobilization by arachidonic acid in trypanosomatids

A recent report (Eintracht J, Maathai R, Mellors A, Ruben L. Calcium entry in Trypanosoma brucei is regulated by phospholipase A(2) and arachidonic ac id, Biochem J 1998;336:659-66) provided evidence that calcium entry in Tryp anosoma brucei bloodstream trypomastigotes is regulated via a signaling pat hway involving phospholipase A(2)-mediated generation of arachidonic acid a nd stimulation of a plasma membrane-located calcium channel. Here we show t hat Ca2+ influx in T. brucei procyclic trypomastigotes, Leishmania donovani promastigotes and T. cruzi amastigotes was also stimulated in a dose-depen dent manner (50-400 nM) by the amphiphilic peptide melittin. This effect wa s blocked by the phospholipase A(2) inhibitor 3-(4-octadecyl)-benzoylacryli c acid. The unsaturated fatty add arachidonic acid, in the range of 10-75 m u M, induced Ca2+ entry by a mechanism sensitive to LaCl3. However, both me littin and arachidonic acid induced an increase in [Ca2+](i) in T. brucei p rocyclic trypomastigotes incubated in Ca2+-free medium implying Ca2+ mobili zation from intracellular stores. This hypothesis was supported by experime nts showing that arachidonic acid promoted Ca2+ release from the acidocalci somes of these cells. The results showing changes in mitochondrial membrane potential. release of acridine orange and Ca2+ from the acidocalcisomes an d Ca2+ transport across the plasma membrane suggest that in addition to the possible stimulation of a Ca2+ channel-mediated process, arachidonic acid, in the range of concentrations used here: have other nonspecific effects o n the trypanosomatids membranes. (C) 2000 Elsevier Science B.V. All rights reserved.